1. Field of the Invention
The present invention relates to a medium transport apparatus, a printer including the medium transport apparatus, a plotter including the medium transport apparatus, and a combination of a printer and a plotter including the medium transport apparatus.
2. Discussion of the Background
Printer is an apparatus for printing on a surface of a sheet-like medium by, for example, ejecting ink droplets from a printer head while moving the printer head in anteroposterior and lateral directions relative to the sheet-like medium. Plotter (cutting plotter) is an apparatus for conducting the cutting process relative to a sheet-like medium by cutting the sheet-like medium into a predetermined shape with a cutter of a cutting head while moving the cutting head in anteroposterior and lateral directions relative to the sheet-like medium. Both apparatuses are already widely used in the industry. There is also known an apparatus having functions as a printer in addition to a plotter (a plotter with print function).
In these apparatuses, an arrangement called “uniaxial medium movement/uniaxial head movement” or an arrangement called “biaxial head movement” is usually employed as a mechanical arrangement for moving a head such as the printer head or the cutting head relative to the sheet-like medium in the anteroposterior and lateral directions. In the “uniaxial medium movement/uniaxial head movement” arrangement, the printing or cutting process is conducted by rotating the feeding roller and the pinch roller in a state that the sheet-like medium is clamped therebetween so as to feed the sheet-like medium in the anteroposterior direction, and moving the head in the lateral direction along the guide rail disposed in parallel with the feeding roller. In the biaxial head movement” arrangement, the printing or cutting process is conducted by moving the head in the anteroposterior and lateral directions.
In an apparatus having the “uniaxial medium movement/uniaxial head movement” arrangement, an important factor for ensuring the printing quality and cutting quality is that the sheet-like medium clamped between the feeding roller and the pinch roller is fed by a precise feeding amount in proportion to the rotation angle of the feeding roller. For preventing partial slippage and looseness of the sheet-like medium, especially a wide and thin sheet-like medium, roller assemblies each having a rotatable pinch roller are disposed above the feeding roller and are arranged at predetermined intervals in the lateral direction. As an example of such roller assemblies, there is an assembly in which the condition of clamping the sheet-like medium is changeable. For example, the assembly includes a clamp switch mechanism to switch between a clamping position where the pinch roller is pressed against the feeding roller to clamp the sheet-like medium and an unclamping position where the pinch roller is spaced apart from the feeding roller to cancel the clamping of the sheet-like medium. JP-A-2006-193303 discloses such an apparatus. The contents of this publication are incorporated herein by reference in their entirety. Further, another assembly includes a clamping pressure setting mechanism which can vary and set the pressing force (sometimes called as “clamping pressure”) of the pinch roller against the feeding roller according to the material and thickness of the sheet-like medium.
However, in the conventional apparatus as mentioned above, an operator operates the appropriate lever whenever the condition of clamping the sheet-like medium is required to be changed. For example, in case that the sheet-like medium is a large leaf (single leaf) sheet-like medium, i.e., that an auto-feeding device such as a sheet feeder is not used, an operator should operate a clamp lever to change the pinch roller from the clamping position to the unclamping position for the purpose of preparing a new sheet-like medium.
In a multifunctional apparatus capable of minutely adjusting the clamping condition according to the material, shape, size, thickness, printing range, and the like of the sheet-like medium, a clamp switch mechanism and a clamping pressure setting mechanism are independently provided for every roller assembly and the clamping pressure can be set to a plurality of stages (for example, three stages such as high, middle, low). Accordingly, in case of processing sheet-like media having different materials, shapes, and/or sizes, it is required to operate the clamp lever and the clamp pressure setting lever of each of the plural roller assemblies for every subject to be processed. Though the multifunction for allowing fine adjustment can be obtained, there is a problem that the setting operation is complex. To solve the problem, there is an idea of providing an arrangement capable of moving the pinch roller and changing the clamping pressure according to an outside signal. However, this arrangement not only makes each roller assembly complex and large but also increases the cost of the entire apparatus and makes the control system complex because this arrangement should be applied to each of the plural roller assemblies.